U.S. patent number 11,066,715 [Application Number 16/086,705] was granted by the patent office on 2021-07-20 for dehydrogenation processing method for turbine blades.
This patent grant is currently assigned to MITSUBISHI POWER, LTD.. The grantee listed for this patent is Mitsubishi Hitachi Power Systems, Ltd.. Invention is credited to Tatsuya Furukawa, Ryuichi Matsubara, Kenji Sato, Yuichi Shimizu.
United States Patent |
11,066,715 |
Shimizu , et al. |
July 20, 2021 |
Dehydrogenation processing method for turbine blades
Abstract
A dehydrogenation processing method for a turbine blade of a
steam turbine. The method includes a step of heating the turbine
blade by suppling heating steam into a casing of the steam turbine
after a steam turbine plant is stopped. The heating steam supplied
to the casing has a temperature that is higher than steam passing
through the turbine blade during operation of the steam turbine
plant. The method further includes repeating the process of
supplying the heating steam into the casing a multiple of
times.
Inventors: |
Shimizu; Yuichi (Tokyo,
JP), Furukawa; Tatsuya (Kanagawa, JP),
Matsubara; Ryuichi (Tokyo, JP), Sato; Kenji
(Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Hitachi Power Systems, Ltd. |
Kanagawa |
N/A |
JP |
|
|
Assignee: |
MITSUBISHI POWER, LTD.
(Kanagawa, JP)
|
Family
ID: |
59964111 |
Appl.
No.: |
16/086,705 |
Filed: |
March 6, 2017 |
PCT
Filed: |
March 06, 2017 |
PCT No.: |
PCT/JP2017/008808 |
371(c)(1),(2),(4) Date: |
September 20, 2018 |
PCT
Pub. No.: |
WO2017/169537 |
PCT
Pub. Date: |
October 05, 2017 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20190100817 A1 |
Apr 4, 2019 |
|
Foreign Application Priority Data
|
|
|
|
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Mar 31, 2016 [JP] |
|
|
JP2016-071719 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01D
9/02 (20130101); F01D 25/00 (20130101); F01D
5/12 (20130101); F01D 25/10 (20130101); C21D
9/00 (20130101); C21D 3/06 (20130101); C21D
1/34 (20130101); F01K 21/06 (20130101); F01K
13/02 (20130101); F05D 2230/40 (20130101); C21D
2211/008 (20130101); F05D 2240/30 (20130101); F05D
2300/701 (20130101); F05D 2300/171 (20130101) |
Current International
Class: |
C21D
3/06 (20060101); F01K 21/06 (20060101); F01D
9/02 (20060101); C21D 1/34 (20060101); C21D
9/00 (20060101); F01K 13/02 (20060101); F01D
25/00 (20060101); F01D 25/10 (20060101); F01D
5/12 (20060101) |
Field of
Search: |
;148/655 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102014221563 |
|
Apr 2016 |
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DE |
|
53-92009 |
|
Aug 1978 |
|
JP |
|
62-159704 |
|
Jul 1987 |
|
JP |
|
2-308903 |
|
Dec 1990 |
|
JP |
|
1990308903 |
|
Dec 1990 |
|
JP |
|
6-306550 |
|
Nov 1994 |
|
JP |
|
6-306551 |
|
Nov 1994 |
|
JP |
|
8-121112 |
|
May 1996 |
|
JP |
|
9-87739 |
|
Mar 1997 |
|
JP |
|
2010159713 |
|
Jul 2010 |
|
JP |
|
5479192 |
|
Apr 2014 |
|
JP |
|
10-1588145 |
|
Jan 2016 |
|
KR |
|
Other References
Translation JP-1990308903 (Year: 1990). cited by examiner .
Translation JP-2010159713-A (Year: 2010). cited by examiner .
Chauhan, Function of Gland Steaming in Turbine Operation (Year:
2016). cited by examiner .
D. Saidi et al. Microstructure and fracture mode of a martensitic
stainless steel steam turbine blade characterized via scanning
auger microscopy and potentiodynamic polarization (Year: 2014).
cited by examiner .
International Search Report dated May 16, 2017 in International
(PCT) Application No. PCT/JP2017/008808, with English translation.
cited by applicant .
International Preliminary Report on Patentability dated Oct. 11,
2018 in International (PCT) Application No. PCT/JP2017/008808, with
English translation. cited by applicant .
Korean Office Action dated Oct. 22, 2019 in corresponding Korean
Patent Application No. 10-2018-7027445 with Machine translation.
cited by applicant .
Examination Report dated Dec. 16, 2019 in corresponding India
Patent Application No. 201817033814. cited by applicant .
Office Action dated Oct. 8, 2020 in corresponding German Patent
Application No. 11 2017 001 657.6. cited by applicant.
|
Primary Examiner: Fung; Coris
Assistant Examiner: Carda; Danielle
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
The invention claimed is:
1. A dehydrogenation processing method for a turbine blade of a
steam turbine, the method comprising: a step of heating the turbine
blade by supplying heating steam into a casing of the steam turbine
after a steam turbine plant is stopped, wherein the heating steam
has a higher temperature than steam passing through the turbine
blade during operation of the steam turbine plant, and repeating
the process of supplying the heating steam into the casing of the
steam turbine, wherein the process of supplying the heating steam
into the casing is repeated multiple times.
2. The dehydrogenation processing method for a turbine blade
according to claim 1, wherein the step of heating the turbine blade
includes supplying gland steam as the heating steam into the casing
via a gland seal portion of the steam turbine.
3. The dehydrogenation processing method for a turbine blade
according to claim 2, wherein the step of heating the turbine blade
includes setting the temperature of the gland steam as the heating
steam to be higher than gland steam during operation of the steam
turbine plant.
4. The dehydrogenation processing method for a turbine blade
according to claim 3, wherein the temperature of the gland steam is
adjusted by a temperature adjuster disposed in a gland steam line
for supplying the gland steam to the gland seal portion.
5. The dehydrogenation processing method for a turbine blade
according to claim 4, wherein the temperature adjuster is a
desuperheater disposed in the gland steam line between a gland
steam header and the gland seal portion, and wherein the
desuperheater is configured to adjust a temperature decrease amount
of the gland steam.
6. The dehydrogenation processing method for a turbine blade
according to claim 5, wherein the step of heating the turbine blade
includes increasing a temperature setting value of the gland steam
at the desuperheater compared to during operation of the steam
turbine plant.
7. The dehydrogenation processing method for a turbine blade
according to claim 2, further comprising: introducing the gland
steam into the casing by supplying the gland steam into the gland
seal portion while maintaining a pressure inside the casing to be
less than an atmospheric pressure; and after heating the turbine
blade, increasing the pressure inside the casing to the atmospheric
pressure, or stopping supply of the gland steam to the gland seal
portion.
8. The dehydrogenation processing method for a turbine blade
according to claim 1, wherein the step of heating the turbine blade
includes heating the turbine blade to a temperature of 120.degree.
C. or higher.
9. The dehydrogenation processing method for a turbine blade
according to claim 1, further comprising: repeating the process of
supplying the heating steam into the casing for multiple times when
the steam turbine plant is stopped, until an accumulated execution
number of the process reaches a predetermined number.
10. The dehydrogenation processing method for a turbine blade
according to claim 1, wherein the turbine blade to be heated
includes a final stage blade of a low-pressure steam turbine.
11. The dehydrogenation processing method for a turbine blade
according to claim 1, wherein the turbine blade is made of
martensitic stainless steel.
Description
TECHNICAL FIELD
The present disclosure relates to a dehydrogenation processing
method for turbine blades of a steam turbine.
BACKGROUND ART
Typically, steel is used for turbine blades of a steam turbine. For
instance, Patent Document 1 discloses a turbine blade using
martensitic stainless steel.
In such turbine blades, there is a risk of occlusion of hydrogen in
the steel depending on the processing procedure. If steel to be
used as turbine blades occludes hydrogen, the turbine blades may
become brittle due to the effect of hydrogen.
CITATION LIST
Patent Literature
Patent Document 1: JPH6-306550A
SUMMARY
Problems to be Solved
Meanwhile, as a general dehydrogenation processing method for
steel, known is baking, where steel is heated to release occluded
hydrogen.
However, in a case where large turbine blades near a final stage of
a steam turbine go through a thermal process, it is necessary to
provide a large thermal processing device, and a considerable
amount of time is required to complete the thermal processing, for
only a limited number of turbine blades can be processed at a
time.
Thus, required is a method whereby it is possible to suppress
hydrogen embrittlement of turbine blades, without performing
complicated works.
An object of at least some embodiments of the present invention is
to provide a dehydrogenation processing method for turbine blades
whereby it is possible to suppress hydrogen embrittlement of
turbine blades, without performing laborious works.
Solution to the Problems
(1) According to at least some embodiments of the present
invention, a dehydrogenation processing method for a turbine blade
of a steam turbine includes: a step of heating the turbine blade by
supplying heating steam into a casing of the steam turbine when a
steam turbine plant is started or stopped.
During operation of a steam turbine plant, the steam temperature at
each position inside the casing is substantially fixed. Thus,
depending on position inside the casing, steam having a relatively
low temperature acts on the turbine blades, and release of hydrogen
from the turbine blades can be barely expected during operation of
the steam turbine plant.
According to the above method (1), heating steam is supplied into
the casing when the steam turbine plant is started or stopped, and
thus it is possible to use heating steam having a suitable
temperature for dehydrogenation processing, unlike when the steam
plant is in operation. Thus, also for the turbine blades that
hardly release hydrogen during operation of the steam turbine
plant, it is possible to perform the dehydrogenation processing, by
causing the turbine blades to make contact with heating steam when
the steam turbine plant is started or stopped.
Accordingly, it is possible to suppress hydrogen embrittlement of
the turbine blades, without performing complicated works such as
removing the turbine blades.
(2) In some embodiments, in the above method (1), the heating steam
has a higher temperature than steam passing through the turbine
blade during operation of the steam turbine (working steam).
Further, by using heating steam having a higher temperature than
working steam that passes through the turbine blades to be
dehydrogenated (to be heated) during operation of the steam turbine
plant (i.e. working steam temperature at the position of the
turbine blades to be dehydrogenated), it is possible to raise the
temperature of the turbine blades more easily, and thus promote
dehydrogenation of the turbine blades.
Herein, in a case where a plurality of stages of turbine blades are
provided in the casing, one or more stages of turbine blades
including the final stage (lowest-pressure stage) may be set as the
turbine blades to be dehydrogenated (to be heated), and the
temperature of the heating steam may be set to be higher than the
working steam temperature at the position of the turbine blades of
the stage to be heated. In this case, the heating steam temperature
may be lower than the temperature of working steam passing through
stages upstream of the stages to be heated.
(3) In some embodiments, in the above method (1) or (2), the step
of heating the turbine blade includes supplying gland steam as the
heating steam into the casing via a gland seal portion of the steam
turbine.
In a typical steam turbine, gland seal portions are supplied with
gland steam, to suppress leakage of steam from the casing interior
space to the casing exterior via a gap between the casing and the
rotor, or entry of air from the casing exterior to the casing
interior space.
According to the above method (3), by utilizing the gland seal
portions and the gland steam system, which are provided for a
typical steam turbine facility, it is possible to introduce gland
steam (heating steam) into the casing readily via the gland seal
portions, when the steam turbine plant is started or stopped and
the pressure of the casing decreases. Thus, it is possible to
perform the dehydrogenation processing for the turbine blades
without providing special equipment to supply heating steam into
the casing.
(4) In some embodiments, in the above method (3), the step of
heating the turbine blade includes setting the temperature of the
gland steam to be higher than gland steam during operation of the
steam turbine.
According to the above method (4), by setting the temperature of
gland steam to be higher than that in operation of the steam
turbine, it is possible to heat the turbine blades to an even
higher temperature, and thereby to perform the dehydrogenation
processing for the turbine blades effectively.
(5) In some embodiments, in the above method (3) or (4), the
temperature of the gland steam is adjusted by a temperature
adjuster disposed in a gland steam line for supplying the gland
steam to the gland seal portion.
According to the above method (5), by adjusting the temperature of
gland steam to be supplied to the gland seal portion with the
temperature adjuster disposed in the gland steam line, it is
possible to control the temperature of the turbine blades in the
dehydrogenation processing, and perform dehydrogenation processing
effectively. Furthermore, it is possible to suppress an excessive
increase in the temperature of the gland steam, and prevent
operation of the interlock related to the gland steam temperature,
for instance.
(6) In some embodiments, in the above method (5), the temperature
adjuster is a desuperheater disposed in the gland steam line
between a gland steam header and the gland seal portion, and the
desuperheater is configured to adjust a temperature decrease amount
of the gland steam.
According to the above method (6), it is possible to adjust the
temperature of gland steam flowing toward the gland seal portion
from the gland steam header appropriately with the desuperheater,
and thereby it is possible to promote dehydrogenation processing
and prevent operation of interlock related to the gland steam
temperature at the same time.
(7) In some embodiments, in the above method (6), the step of
heating the turbine blade includes increasing a temperature setting
value of the gland steam at the desuperheater compared to during
operation of the steam turbine.
According to the above method (7), by setting the temperature
setting value of gland steam at the desuperheater to be higher than
that in operation of the steam turbine, it is possible to heat the
turbine blades to an even higher temperature, and thereby to
perform the dehydrogenation processing effectively.
(8) In some embodiments, in any one of the above methods (3) to
(7), the method further includes: introducing the gland steam into
the casing by supplying the gland steam into the gland seal portion
while maintaining a pressure inside the casing to be less than an
atmospheric pressure; and, after heating the turbine blade,
increasing the pressure inside the casing to the atmospheric
pressure, or stopping supply of the gland steam to the gland seal
portion.
According to the above method (8), it is possible to introduce
gland steam easily into the casing by supplying gland steam to the
gland seal portions while maintaining the pressure in the casing to
be less than the atmospheric pressure. Thus, it is possible to fill
the casing with high-temperature gland steam, and heat the turbine
blades effectively with the gland steam.
(9) In some embodiments, in any one of the above methods (1) to
(8), the step of heating the turbine blade includes heating the
turbine blade to a temperature of 120.degree. C. or higher.
As a result of intensive researches by the present inventors, it
was found that the hydrogen content in the turbine blades decreases
significantly by heating the turbine blades to a temperature of
120.degree. C. or higher.
Thus, according to the above method (9), it is possible to perform
dehydrogenation processing on the turbine blades effectively by
increasing the temperature of the turbine blades to 120.degree. C.
or higher.
(10) In some embodiments, in any one of the above methods (1) to
(9), the method further comprises repeating a process of supplying
the heating steam into the casing for multiple times.
As a result of intensive researches by the present inventors, it
was found that the hydrogen content in the turbine blades decreases
considerably by repeating the heating process for the turbine
blades multiple times.
According to the above method (10), it is possible to perform the
dehydrogenation processing on the turbine blades effectively by
repeating the heating process for the turbine blades multiple
times.
(11) In some embodiments, in the above method (10), the method
further includes repeating the process of supplying the heating
steam into the casing for multiple times when the steam turbine
plant is started or stopped, until an accumulated execution number
of the process reaches a predetermined number.
According to the above method (11), it is possible to perform the
dehydrogenation processing for the turbine blades effectively, by
repeating the heating process for the turbine blades until the
accumulation execution number of the heating process reaches a
predetermined number.
Herein, "predetermined number" is typically two or more, and may be
set individually depending on the type of the steam turbine, the
gland steam temperature, and the like.
(12) In some embodiments, in any one of the above methods (1) to
(11), the turbine blade to be heated includes a final stage blade
of a low-pressure steam turbine.
During operation of the steam turbine, steam having a low
temperature such as about 50.degree. C. acts on the final stage
blades of the low-pressure steam turbine. Thus, release of hydrogen
from the turbine blades can be barely expected during operation of
the steam turbine.
In this regard, according to the above method (12), as described in
the above (1), it is possible to suppress hydrogen embrittlement of
the final stage blades of the low-pressure turbine, without
performing complicated works such as removing the turbine blades,
by supplying heating steam into the casing when the steam turbine
plant is started or stopped.
(13) In some embodiments, in any one of the above methods (1) to
(12), the turbine blade is made of martensitic stainless steel.
According to findings of the present inventors, martensitic
stainless steel used to make the turbine blades tends to become
brittle when the hydrogen content increases.
In this regard, according to the above method (13), as described in
the above (1), it is possible to prevent damage due to hydrogen
embrittlement of the turbine blades made of martensitic stainless
steel, without performing complicated works such as removing the
turbine blades, by supplying heating steam into the casing when the
steam turbine plant is started or stopped.
Advantageous Effects
According to at least some embodiments of the present invention,
also for the turbine blades that hardly release hydrogen during
operation of the steam turbine plant, it is possible to perform
dehydrogenation processing, by causing the turbine blades to make
contact with heating steam when the steam turbine plant is started
or stopped. Accordingly, it is possible to suppress hydrogen
embrittlement of the turbine blades, without performing complicated
works such as removing the turbine blades.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a cross-sectional view of a steam turbine according to an
embodiment.
FIG. 2 is a flowchart of a dehydrogenation processing method for
turbine blades according to an embodiment.
FIG. 3 is a graph showing an example of temporal change of the
turbine blade temperature and the rotation speed of the steam
turbine.
FIG. 4 is a graph showing the temporal change of the turbine blade
temperature, the rotation speed of the steam turbine, the casing
vacuum degree (if supply of heating steam is stopped), according to
an embodiment.
FIG. 5 is a graph showing the temporal change of the turbine blade
temperature, the rotation speed of the steam turbine, the casing
vacuum degree (if vacuum break is performed), according to another
embodiment.
FIG. 6 is a graph showing a result of an evaluation test of a
dehydrogenation effect on turbine blades.
FIG. 7 is a schematic configuration diagram of a gland system (in
high-load operation) according to an embodiment.
FIG. 8 is a schematic configuration diagram of a gland system (when
heating turbine blades) according to an embodiment.
DETAILED DESCRIPTION
Embodiments of the present invention will now be described in
detail with reference to the accompanying drawings. It is intended,
however, that unless particularly identified, dimensions,
materials, shapes, relative positions and the like of components
described in the embodiments shall be interpreted as illustrative
only and not intended to limit the scope of the present
invention.
First, with reference to FIG. 1, a schematic configuration of a
steam turbine 1 will be described as an example of application of
the dehydrogenation processing method for turbine blades according
to the present embodiment. Herein, FIG. 1 is a cross-sectional view
of a steam turbine 1 according to an embodiment. The steam turbine
1 is provided for a plant such as a thermal power generation plant,
for instance.
In some embodiments, the steam turbine 1 includes a casing 2, a
rotor 5 disposed so as to penetrate through the casing 2, turbine
blades 10 including a plurality of rotor blades 8 and a plurality
of stationary vanes 9, and gland seal portions 22a, 22b for
suppressing leakage of steam from a casing interior space 3.
The casing 2 includes a casing inlet 2a disposed on the first side
in the axial direction of the rotor 5, for introducing steam into
the casing 2, and a casing outlet 2b disposed on the second side,
for discharging steam after having performed work.
The rotor 5 is supported by bearings 7a, 7b so as to be rotatable
about the axis O.
The plurality of rotor blades 8 are mounted to the rotor 5 via a
turbine disc 6, so as to be arranged in the circumferential
direction of the rotor 5. The plurality of rotor blades 8 are
disposed in a plurality of stages in the axial direction of the
rotor 5, thereby forming rotor blade rows.
The plurality of stationary vanes 9 are mounted to the inner
surface of the casing 2, so as to be arranged in the
circumferential direction of the casing 2. The plurality of
stationary vanes 9 are disposed in a plurality of stages
alternately with the rotor blade rows in the axial direction of the
rotor 5, thereby forming stationary vane rows.
The casing outlet 2b of the steam turbine 1 may be in communication
with a condenser (not depicted).
The gland seal portions 22a, 22b are provided to suppress leakage
of steam from the casing interior space 3 to the casing exterior 4
via a gap between the casing 2 and the rotor 5, or entry of air
from the casing exterior 4 to the casing interior space 3. The
gland seal portions 22a, 22b are disposed on the first side (the
side of the casing inlet 2a) and the second side (the side of the
casing outlet 2b) of the casing 2 in the axial direction of the
rotor 5, respectively. The gland seal portions 22a, 22b are
disposed in gland cases 23a, 23b disposed between the rotor through
hole of the casing 2 and the outer peripheral surface of the rotor
5, respectively. In the depicted example, the high-pressure side
gland seal portion 22a is disposed on the high-pressure side (the
side of the casing inlet 2a) of the casing interior space 3, and
the low-pressure side gland seal portion 22b is disposed on the
low-pressure side (the side of the casing outlet 2b) of the casing
interior space 3.
In the steam turbine 1 having the above configuration, during
normal operation, steam introduced into the casing interior space 3
from the casing inlet 2a flows through the casing interior space 3
while passing through the plurality of turbine blades (rotor blades
8 and stationary vanes 9) 10, and thereby a rotational force is
generated on the rotor 5. Further, steam after having performed
work is discharged to the outside from the casing interior space 3
through the casing outlet 2b.
At this time, the gland seal portions 22a, 22b are supplied with
gland steam. Accordingly, it is possible to ensure the sealing
performance of the gap between the casing 2 and the rotor 5,
thereby suppressing leakage of steam from the casing interior space
3 to the casing exterior 4, or entry of air from the casing
exterior 4 to the casing interior space 3.
Next, with reference to FIG. 2, the dehydrogenation processing
method for turbine blades according to some embodiments will be
described. Herein, FIG. 2 is a flowchart of a dehydrogenation
processing method for turbine blades according to an embodiment. In
the following description, each component of the steam turbine 1 is
indicated by the same reference numeral shown in FIG. 1.
In the embodiment shown in FIG. 2, shown is an exemplary embodiment
where the turbine blades 10 are heated when the steam turbine 1 is
stopped. Nevertheless, in another embodiment, the turbine blades 10
may be heated when the steam turbine 1 is started.
As shown in FIG. 2, the dehydrogenation processing method for
turbine blades according to some embodiments includes a step (S4)
of heating the turbine blades 10 by supplying heating steam into
the casing 2 of the steam turbine 1 when the steam turbine 1 is
stopped (S2) or started.
For instance, in the embodiment shown in FIG. 2, the steam turbine
1 is operated (S1), and then the steam turbine 1 is stopped (S2).
After the steam turbine 1 is stopped, heating steam is supplied
into the casing 2 of the steam turbine 1 to heat the turbine blades
10 (S4).
In the above method, heating steam supplied into the casing 2 of
the steam turbine 1 may have a higher temperature than steam that
passes through the turbine blades 10 during operation of the steam
turbine 1 (working steam). More specifically, heating steam may
have a higher temperature than working steam at a location to which
the heating steal is supplied.
The heating steam to be supplied into the casing 2 of the steam
turbine 1 is not particularly limited, and may be gland steam
described below, or another steam generated in the plant in which
the steam turbine 1 is installed. The other steam may be steam
drawn from an auxiliary steam system of the plant, for instance, or
steam extracted from a mid-pressure turbine or a high-pressure
turbine.
Further, the heating time of the turbine blades 10, that is,
duration of supply of heating steam into the casing 2, may be
longer than that in a case where the dehydrogenation processing is
not performed on the turbine blades 10. Specifically, the heating
time of the turbine blades 10 may be set on the basis of at least
one of the concentration of hydrogen contained in the turbine
blades 10, the thickness of the turbine blades 10, the temperature
of the heating steam, or the flow rate of the heating steam. For
instance, the heating time of the turbine blades 10 may be not
shorter than 12 hours and not longer than 24 hours.
During operation of the steam turbine 1, the steam turbine at each
position inside the casing is substantially fixed. Thus, depending
on position inside the casing 2, steam having a relatively low
temperature acts on the turbine blades 10, and release of hydrogen
from the turbine blades 10 can be barely expected during operation
of the steam turbine 1.
According to the above method, heating steam is supplied into the
casing 2 when the steam turbine 1 is started or stopped, and thus
it is possible to use heating steam having a suitable temperature
for dehydrogenation processing, unlike when the steam turbine 1 is
in operation. Thus, also for the turbine blades 10 that hardly
release hydrogen during operation of the steam turbine 1, it is
possible to perform the dehydrogenation processing, by causing the
turbine blades 10 to make contact with heating steam when the steam
turbine 1 is started or stopped. In particular, the rotor blades 8
tend to occlude hydrogen at the time of manufacture, and thus it is
possible to remove hydrogen effectively from the rotor blades 8
through the above method.
Accordingly, it is possible to suppress hydrogen embrittlement of
the turbine blades 10, without performing complicated works such as
removing the turbine blades 10.
Further, by using heating steam having a higher temperature than
working steam, it is possible to raise the temperature of the
turbine blades 10 more easily, and thus promote dehydrogenation of
the turbine blades 10.
In an embodiment, in the step of heating the turbine blades 10 as
shown in FIG. 2 (S4), the turbine blades 10 may be heated to a
temperature of 120.degree. C. or higher (see FIGS. 3 to 5).
For instance, as shown in FIG. 3, when supply of steam to the steam
turbine 1 is stopped, the rotation speed of the steam turbine 1
decreases rapidly. Then, when heating steam is supplied to the
casing 2, the turbine blade temperature gradually increases with
time after stop. Herein, FIG. 3 is a graph showing an example of
temporal change of the turbine blade temperature and the rotation
speed of the steam turbine.
As a result of intensive researches by the present inventors, it
was found that the hydrogen content in the turbine blades 10
decreases significantly by heating the turbine blades 10 to a
temperature of 120.degree. C. or higher.
Thus, according to the above method, it is possible to perform
dehydrogenation processing on the turbine blades 10 effectively by
increasing the temperature of the turbine blades 10 to 120.degree.
C. or higher.
Furthermore, in view of the heat resistance property of the turbine
blades 10 and other components of the casing, the heating steam may
be supplied so that the temperature of the turbine blades 10 does
not exceed 180.degree. C.
In the step of heating the turbine blades 10 (S4), the process of
supplying heating steam into the casing 2 may be repeated multiple
times.
In this case, the process of supplying heating steam into the
casing 2 may be repeated until the accumulation execution number of
the heating process (S4) of the turbine blades 10 reaches a
predetermined number.
For instance, in the embodiment shown in FIG. 2, after stopping
operation of the steam turbine 1 (S2), it is determined whether the
accumulation execution number of the heating process (S4) of the
turbine blades 10 after the initial state of the steam turbine 1 is
not smaller than a predetermined number (S3). If the accumulation
execution number of the heating process for the turbine blades 10
is not smaller than a predetermined number, the heating process for
the turbine blades 10 (S4) is not performed. On the other hand, if
the accumulation execution number of the heating process for the
turbine blades 10 is smaller than a predetermined number, the
heating process for the turbine blades 10 (S4) is performed by
supplying heating steam into the casing 2. Further, after the
elapse of a setting time from heating of the turbine blades 10,
vacuum break is performed, or supply of heating steam is stopped
(S5).
Then, operation of the steam turbine 1 is restarted when needed
(S1), and when the steam turbine 1 is to be stopped (S2), it is
determined again whether the accumulation execution number of the
heating process for the turbine blades 10 is not smaller than the
predetermined number (S3). The above steps are repeated until the
accumulation execution number of the heating process for the
turbine blades 10 reaches the predetermined number.
Herein, "predetermined number" is typically two or more, and may be
set individually depending on the type of the steam turbine, the
gland steam temperature, and the like.
FIG. 4 is a graph showing the temporal change of the turbine blade
temperature, the rotation speed of the steam turbine, the casing
vacuum degree (if supply of heating steam is stopped), according to
an embodiment. FIG. 5 is a graph showing the temporal change of the
turbine blade temperature, the rotation speed of the steam turbine,
the casing vacuum degree (if supply of heating steam is stopped),
according to another embodiment.
In the embodiment shown in FIG. 4, after operation of the steam
turbine 1 is stopped, heating steam is supplied into the casing 2,
and the supply of heating steam is stopped after a predetermined
period of time. By supplying heating steam into the casing 2, the
turbine blade temperature increases gradually, and once the supply
of heating steam is stopped, the turbine blade temperature
decreases.
In the embodiment shown in FIG. 5, after operation of the steam
turbine 1 is stopped, heating steam is supplied into the casing 2,
and vacuum break is performed after a predetermined period of time.
By supplying heating steam into the casing 2, the turbine blade
temperature increases gradually, and after the vacuum break, the
turbine blade temperature decreases. In this case, the supply of
heating steam may be stopped after vacuum break.
Herein, vacuum break refers to, in a case where a condenser (not
depicted) is disposed in a latter stage of the steam turbine 1,
opening a vacuum break valve of the condenser to bring the pressure
inside the casing 2 closer to the atmospheric pressure.
As a result of intensive researches by the present inventors, it
was found that the hydrogen content in the turbine blades 10
decreases considerably by repeating the heating process for the
turbine blades 10 multiple times.
Herein, FIG. 6 shows a result of an evaluation test of the
dehydrogenation effect achieved by the above described heating
process on the turbine blades 10. FIG. 6 shows a hydrogen
concentration at the time when stainless steel occluding 4.3 ppm
hydrogen is heated to a temperature higher than 120.degree. C. As
shown in the graph, the hydrogen concentration decreases to 0.24
ppm when the heating process is performed once, and to 0.03 ppm
when the heating process is repeated five times.
According to the above method, it is possible to perform the
dehydrogenation processing on the turbine blades 10 effectively by
repeating the heating process for the turbine blades multiple
times.
Further, it is possible to perform the dehydrogenation processing
for the turbine blades 10 effectively, by repeating the heating
process until the accumulation execution number of the heating
process for the turbine blades 10 reaches a predetermined
number.
Further, the heating process may be less frequent if the turbine
blades 10 have a low hydrogen concentration in the initial state or
if the turbine blades 10 have a relatively small thickness.
In the above method, the turbine blades 10 to be heated may include
final stage blades of the low-pressure steam turbine (e.g. final
stage rotor blades 8a depicted in FIG. 1).
During operation of the steam turbine 1, steam having a low
temperature such as about 50.degree. C. acts on the final stage
blades of the low-pressure steam turbine. Thus, release of hydrogen
from the turbine blades 10 can be barely expected during operation
of the steam turbine 1.
In this regard, according to the above method, as described above,
it is possible to suppress hydrogen embrittlement of the final
stage blades of the low-pressure steam turbine, without performing
complicated works such as removing the turbine blades 10, by
supplying heating steam into the casing 2 when the steam turbine 1
is started or stopped.
In the above method, the turbine blades 10 may be martensitic
stainless steel. For instance, martensitic stainless steel
includes, for instance, Ph13-8Mo steel, 17-4PH steel, and 12cr
steel.
According to findings of the present inventors, martensitic
stainless steel used to make the turbine blades 10 tends to become
brittle when the hydrogen content increases.
In this regard, as described above, it is possible to prevent
damage due to hydrogen embrittlement of the turbine blades 10 made
of martensitic stainless steel, without performing complicated
works such as removing the turbine blades 10, by supplying heating
steam into the casing when the steam turbine 1 is started or
stopped.
In the above described step of heating the turbine blades 10 (S4),
as shown in FIGS. 7 and 8, gland steam may be supplied into the
casing 2 as heating steam, via the gland seal portions 22a, 22b of
the steam turbine 1.
Next, with reference to FIGS. 7 and 8, a specific configuration
example of a gland system 20 will be described. FIG. 7 is a
schematic configuration diagram of a gland system (in high-load
operation) 20 according to an embodiment. FIG. 8 is a schematic
configuration diagram of a gland system (when heating turbine
blades) 20 according to an embodiment.
In the following description, each component of the steam turbine 1
is described with the same reference numeral shown in FIG. 1, where
appropriate.
As shown in FIGS. 7 and 8 as an example, the gland system 20
according to some embodiments includes the above described gland
seal portions 22a, 22b, a gland steam header 24 for storing gland
steam to be supplied to the gland seal portions 22a, 22b, and gland
steam lines 28, 29 disposed between the gland steam header 24 and
the gland seal portions 22a, 22b.
In the present embodiment, gland steam refers to steam that flows
through the gland seal portions 22a, 22b and thereby functions to
ensure the sealing performance between the casing interior space 3
and the casing exterior 4. That is, gland steam includes steam that
flows from the casing interior space 3 to the casing exterior 4 via
the gland seal portions 22a, 22b, respectively.
The gland steam header 24 is configured to store gland steam to be
supplied to the gland seal portions 22a, 22b. For instance, the
gland steam stored in the gland steam header 24 may be steam drawn
from an auxiliary steam system of the plant, steam extracted from
e.g. the mid-pressure turbine or the high-pressure turbine, or
steam obtained by depressurizing turbine-inlet steam. Further,
gland steam may contain steam recovered from the high-pressure side
gland seal portion 22a at a high-load time. Moreover, gland steam
may include combination of more than one types of steam from
different sources as described above.
As shown in FIG. 7, during high-load operation of the steam turbine
1, the casing interior pressure is relatively high, and thus steam
(gland steam) flows out from the casing interior space 3 toward the
casing exterior 4 at the high-pressure side gland seal portion 22a.
At least a part of the gland steam is recovered by the gland steam
header 24 via the gland steam line 28. Further, at least another
part of the gland steam may be guided to a gland condenser to be
condensed. For instance, a part of the flown-out gland steam is
recovered by the gland steam header 24 from the casing-side portion
X of the high-pressure side gland seal portion 22a, and the
remainder of the flown-out gland steam is guided to the gland
condenser from the atmosphere-side portion Y.
Furthermore, the low-pressure side gland seal portion 22b is
supplied with gland steam from the gland steam header 24. Further,
at least another part of the gland steam flowing out from the
low-pressure side gland seal portion 22b may be guided to a gland
condenser. For instance, the gland steam is supplied to the
casing-side portion X of the low-pressure side gland seal portion
22b from the gland steam header 24, and a part of the supplied
gland steam (containing air) is guided to the gland condenser from
the atmosphere-side portion Y of the low-pressure side gland seal
portion 22b.
Furthermore, during low-load operation or no-load operation of the
steam turbine 1, the high-pressure side gland seal portion 22a is
also supplied with gland steam from the gland steam header 24.
As shown in FIG. 8, in the heating process for the turbine blades
10, the gland steam from the gland steam header 24 is supplied to
the gland seal portions 22a, 22b via the gland steam lines 28, 29.
At this time, the casing interior pressure is relatively low, and
thus the gland steam is supplied into the casing 2 via the gland
seal portions 22a, 22b. For instance, gland steam is supplied from
the gland steam header 24 to the casing-side portion X of the
high-pressure side gland seal portion 22a and the casing-side
portion X of the low-pressure side gland seal portion 22b.
Furthermore, a part of the supplied gland steam (containing air) is
guided to the gland condenser from the atmosphere-side portion Y of
the high-pressure side gland seal portion 22a and the
atmosphere-side portion Y of the low-pressure side gland seal
portion 22b.
According to this method, by utilizing the gland seal portions 22a,
22b and the gland steam system (gland steam header 24, gland steam
lines 28, 29, etc.), which are provided for a typical steam turbine
facility, it is possible to introduce gland steam (heating steam)
into the casing 2 readily via the gland seal portions 22a, 22b,
when the steam turbine 1 is started or stopped and the pressure of
the casing 2 decreases. Thus, it is possible to perform the
dehydrogenation processing for the turbine blades 10 without
providing special equipment to supply heating steam into the casing
2.
As shown in FIGS. 7 and 8, a discharge line 25 having a relief
valve 26 may be connected to the gland steam header 24, to prevent
an excessive pressure increase inside the gland steam header 24. In
this case, if the pressure in the gland steam header 24 exceeds a
setting value, the relief valve 26 opens and discharges gland steam
from the discharge line 25.
In the above method, in the heating process for the turbine blades
10, the temperature of gland steam may be set to be higher than
that during operation of the steam turbine 1. That is, the
temperature of gland steam used in the heating process for the
turbine blades 10 is set to be higher than the temperature of steam
supplied to the gland seal portions 22a, 22b during operation of
the steam turbine 1. For instance, steam supplied to the gland
steam header 24 may have a higher temperature than that during
operation of the steam turbine 1, or the gland steam may be heated
between the gland steam header 24 and the gland seal portions 22a,
22b when being supplied, as described below.
Accordingly, by setting the temperature of gland steam to be higher
than that in operation of the steam turbine 1, it is possible to
heat the turbine blades 10 to an even higher temperature, and
thereby to perform the dehydrogenation processing for the turbine
blades 10 effectively.
Further, the temperature of the gland steam may be adjusted by a
temperature adjuster disposed in the gland steam line 29 for
supplying gland steam to the gland seal portions 22a, 22b.
In this case, as shown in FIG. 8, the temperature adjuster may be a
desuperheater 30 disposed in the gland steam line 29 between the
gland steam header 24 and the gland seal portions 22a, 22b, and the
temperature decrease amount of the gland steam may be adjusted by
the desuperheater 30. For instance, the desuperheater 30 may cool
the gland steam by performing indirect heat exchange with cooling
water. In this case, the temperature of the turbine blades 10 may
be detected by the temperature sensor 36, and the opening degree of
a flow-rate adjustment valve 31 may be controlled by a control
device 35 on the basis of the temperature, to adjust the flow rate
of cooling water for cooling the gland steam.
In another non-depicted embodiment, the temperature adjuster may be
a heater for heating the gland steam.
Accordingly, by adjusting the temperature of gland steam to be
supplied to the gland seal portions 22a, 22b with the temperature
adjuster disposed in the gland steam line 29, it is possible to
control the temperature of the turbine blades 10 during the
dehydrogenation processing, and perform dehydrogenation processing
effectively. Furthermore, it is possible to suppress an excessive
increase in the temperature of the gland steam, and prevent
operation of the interlock related to the gland steam temperature,
for instance.
Further, by using the desuperheater 30 as the temperature adjuster,
it is possible to adjust the temperature of gland steam flowing
toward the gland seal portions 22a, 22b from the gland steam header
appropriately with the desuperheater 30, and thereby it is possible
to promote dehydrogenation processing and prevent operation of
interlock related to the gland steam temperature at the same
time.
In the above method, in the heating process for the turbine blades
10, the temperature setting value for gland steam in the
desuperheater 30 may be higher than that during operation of the
steam turbine 1.
Accordingly, by setting the temperature setting value of gland
steam in the desuperheater 30 to be higher than that in operation
of the steam turbine 1, it is possible to heat the turbine blades
10 to an even higher temperature, and thereby to perform the
dehydrogenation processing effectively.
As shown in FIG. 8, a drain separator 32 may be disposed in the
gland steam line 29, on the side closer to the low-pressure side
gland seal portion 22b than the desuperheater 30.
The drain separator 32 is configured to separate drain generated
from condensation of a part of gland steam in the desuperheater
30.
Accordingly, by separating drain generated from condensation of a
part of gland steam in the desuperheater 30 with the drain
separator 32, it is possible to prevent entry of drain to the
casing 2.
In the embodiment shown in FIGS. 7 and 8, the desuperheater 30 and
the drain separator 32 are disposed only in the gland steam line 29
for supplying gland steam to the low-pressure side gland seal
portion 22b. Nevertheless, the desuperheater 30 and the drain
separator 32 may be disposed also in the gland steam line 28 for
supplying gland steam to the high-pressure side gland seal portion
22a.
Further, in the above method, gland steam may be supplied to the
gland seal portions 22a, 22b while maintaining the pressure inside
the casing 2 to be less than the atmospheric pressure, so as to let
gland steam flow into the casing 2 and increase the pressure inside
the casing 2 to the atmospheric pressure after heating the turbine
blades 10, or stop supply of gland steam to the gland seal portions
22a, 22b (see FIG. 5).
According to this method, it is possible to introduce gland steam
easily into the casing 2 by supplying gland steam to the gland seal
portions 22a, 22b while maintaining the pressure in the casing 2 to
be less than the atmospheric pressure. Thus, it is possible to fill
the casing 2 with high-temperature gland steam, and heat the
turbine blades 10 effectively with the gland steam.
As described above, according to at least some embodiments of the
present invention, also for the turbine blades 10 that hardly
release hydrogen during operation of the steam turbine 1, it is
possible to perform the dehydrogenation processing, by causing the
turbine blades 10 to make contact with heating steam when the steam
turbine 1 is started or stopped. Accordingly, it is possible to
suppress hydrogen embrittlement of the turbine blades 10, without
performing complicated works such as removing the turbine blades
10.
Embodiments of the present invention were described in detail
above, but the present invention is not limited thereto, and
various amendments and modifications may be implemented.
For instance, while a single-flow steam turbine is depicted in FIG.
1, where working steam enters from the casing inlet 2a and then
flows in a single direction (in the drawing, from left to right),
the above description of the embodiments can be also applied to a
double-flow steam turbine, where working steam enters from a casing
inlet and flows in both directions.
For instance, an expression of an equal state such as "same"
"equal" and "uniform" shall not be construed as indicating only the
state in which the feature is strictly equal, but also includes a
state in which there is a tolerance or a difference that can still
achieve the same function.
On the other hand, an expression such as "comprise", "include",
"have", "contain" and "constitute" are not intended to be exclusive
of other components.
REFERENCE SIGNS LIST
1 Steam turbine 2 Casing 5 Rotor 8 Rotor blade 9 Stationary vane 10
Turbine blade 20 Gland system 22a High-pressure side gland seal
portion 22b Low-pressure side gland seal portion 23a, 23b Gland
case 24 Gland steam header 28, 29 Gland steam line 30 Desuperheater
31 Flow-rate adjustment valve 32 Drain separator
* * * * *